1. Field of the Invention
The present invention relates to transparent high barrier multilayer structures. Specifically, the present invention relates to a transparent high barrier pouch composed of a multilayer film structure having at least one layer of a polymer with a metal oxide deposition thereon.
2. Description of the Related Art
High barrier flexible materials for packaging strive for glass-like properties without the weight associated with glass containers. Many inventions have been developed which attempt to reach this "Holy Grail" of the packaging industry. For example, Lofgren et al, U.S. Pat. No. 5,122,410, for a Laminated Packing Material With Gas and Aroma Barrier Properties discloses a laminate of two thermoplastic layers, each coated with a silicon compound, bonded together by an intermediate layer of an adhesive agent. The silicon compound may be SiO.sub.2 which provides good gas and aroma barrier properties for packages fabricated from the laminate.
Deak et al, U.S. Pat. No. 5,085,904 for Barrier Materials Useful For Packaging discloses a multilayer structure of a 10-75 nanometer thick layer of SiO vacuum deposited on a resin substrate of either polyester or polyamide with at least a 20 nanometer thick layer of SiO.sub.2 vacuum deposited on the SiO layer. Deak et al specifically teaches "the necessity of the SiO/SiO.sub.2 multilayer combination in terms of barrier properties." Deak et al further teaches that "it is essential that some thickness of SiO layer be present, since it is the combination of resin substrate and the SiO and SiO.sub.2 layers that provides the desirable barrier properties." Deak et al also teaches that the use of SiO will impart a yellow coloration which may not be perceptible if the SiO layer is very thin. However, at these small thickness the SiO layer provides virtually no barrier properties unless combined with a SiO.sub.2 layer. Deak et al also teaches that the use of SiO.sub.2 alone is limited due to decreasing flexibility with increasing thickness. Thus, according to Deak et al, only a multilayer structure of a 10-75 nanometer thick layer of SiO vacuum deposited on a resin substrate of either polyester or polyamide with at least a 20 nanometer thick layer of SiO.sub.2 vacuum deposited on the SiO layer will exhibit sufficient barrier properties with an acceptable flexibility.
The foregoing patents, although efficacious in the protection of their contents, are not the denouement of the problems of the packaging industry. There are still unresolved problems which compel the enlargement of inventions in the packaging industry.